Derivatography as the Method of Water Structure Studying on Solid Mineral Surface
January 10, 2020
The actual problem of the dewatering and fine dispersing materials process intensification is the development of reliable methods for valuation of water structure on solid mineral surface (especially, coal surface). Thus the question of correlation determination between the amount of superficial moisture which can be mechanically removed, stands especially roughly and that, which is not removable by mechanical methods – filtration, centrifugal etc. The last has presented by the structured (limited) pellicles.
Earlier this problem was studied by line of authors (Bochkov 1996; Bejlin 1969; Ivanova 1974; Derivatogramms 1992; Kazanskij 1961 & Deriagin 1989), but qualitative and quantitative estimation of the pellicle moisture remains ambiguous. Nowadays there is a line of quantitative estimation methods for different types of moisture. First of all, there are methods for efficiently determination of strongly combined (hygroscopic) moisture, for example according to GOST 8719-70 and its equivalents (Bejlin 1969). As for other moisture forms, the lack of clear bounders between separate moisture types (according to connection of energetic indexes “solid liquid”) leads to difficulty of quantitative appreciation.
Secondly, there is an attempt of moisture types of identification and their quantitative determination, which is made in (Bejlin 1969 & Kazanskij 1961) with help of isothermal drying thermo-grams of silica gel. According to M.I. Bejlin (Bejlin 1969) thermo-grams allow to differ various kinds of capillary moisture: “internal capillary moisture” (moisture of capillary escalation); capillary joint moisture and hygroscopic moisture too. By the method what we meant, the identification of strongly combined moisture is difficult in according to non-clear thermo-grams bends of mineral system drying. Thirdly, nowadays the unique method of moisture determination, which not retire by mechanical methods, is the method of maximal molecular moisture capacity (MMMC) (Bochkov 1996). What is widely used on the theory and in the practice. This method is an integral estimation of row species moisture such as: capillary, internal and partly external, film moisture, which cannot be excised mechanically.
Their differential estimation by MMMC method is impossible. Having a concrete practical meaning, this method is of little use for theoretical analysis of different moisture types. Thus, our short survey demonstrates the presence the individual methods for estimation of different moisture types and the limits of their usage. At the same time, so named “thin” and “thick” moisture pellicle (anot speaking about their possible elements) cannot be identified by known methods, although exactly they roughly differ by the energy of connection with a hard surface from others (Deriagin 1989).
EXPOSITION OF BASIC MATERIAL
On the practice, physical-chemical investigations of minerals and especially coal, the method of derivatography is widely used (Ivanova 1974 &; Derivatogramms 1992). One of its functions is determination of moisture and hydroxides content in minerals (Derivatogramms 1992). The derivatography usage for estimation of water phase structure on coal surface was offered by us. For this, coal analytical samples of stamp “Ж (fat)” from mine “Samsonivska-Zahidna #1” were investigated with ash content 9.5%. Fresh crashed coal and oxidized on air by 20 оС was used, during one month. Experiments were duplicated for coincidence determination of results. For moisturizing coal had been used water with pH 7.
How you can see, the maximums of water evacuation for samples sufficiently differ by intensity, configuration, especially extent of symmetry and area under curves. Let’s stay on this characteristic more detailed. Intensity of DTG peaks by its nature determinates the maximal speed of oistureremoving, and area under curve shows the mass of moisture what is re moved. The effect of non-symmetry is connected with the existence of different moisture kinds on coal surface. So as different kinds of moisture have various energy of connection with solid surface, that is why they are removed in different temperature intervals. Especially here, different temperatures take place, which are corresponding to maximal speed of moisture-removing for different kinds of moisture (points on basic line, what are corresponding to tops of peaks). Every kind of moisture IS characterized by its own peak of moisture-removing (in definite temperature intervals) and their overlay leads to non-symmetric peaks on DTG. That is why, to decompose non-symmetric peaks of DTG to Gauss curves allows to identify separate moisture forms. Let’s analyze these peaks of moisture-removing, using DTG – curves.
Peaks of moisture-removing for air dry coal (sample 1, Figure 2a) has small intensity, “soft” fronts of DTG, it is practically symmetric. The last (symmetric), obviously, attested to homogeneous water structure, which in this case represents only as pellicle moisture. Small intensity (amplitude) and some plane of peak leads to low rate of moistureremoving. This fact is exactly characterized for strongly combined moisture. Additionally, maximal rate of moisture-removing is observed at higher temperature (135 оС), that also testifies the highpower connection of contacting phases “watersolid”.